error: can't start new thread

Question

I have a site that runs with follow configuration:

Django + mod-wsgi + apache

In one of user's request, I send another HTTP request to another service, and solve this by httplib library of python.

But sometimes this service don't get answer too long, and timeout for httplib doesn't work. So I creating thread, in this thread I send request to service, and join it after 20 sec (20 sec - is a timeout of request). This is how it works:

class HttpGetTimeOut(threading.Thread):     def __init__(self,**kwargs):         self.config = kwargs         self.resp_data = None         self.exception = None         super(HttpGetTimeOut,self).__init__()     def run(self):          h = httplib.HTTPSConnection(self.config['server'])         h.connect()         sended_data = self.config['sended_data']         h.putrequest("POST", self.config['path'])         h.putheader("Content-Length", str(len(sended_data)))         h.putheader("Content-Type", 'text/xml; charset="utf-8"')         if 'base_auth' in self.config:             base64string = base64.encodestring('%s:%s' % self.config['base_auth'])[:-1]             h.putheader("Authorization", "Basic %s" % base64string)         h.endheaders()          try:             h.send(sended_data)             self.resp_data = h.getresponse()         except httplib.HTTPException,e:             self.exception = e         except Exception,e:             self.exception = e 

something like this...

And use it by this function:

getting = HttpGetTimeOut(**req_config) getting.start() getting.join(COOPERATION_TIMEOUT) if getting.isAlive(): #maybe need some block     getting._Thread__stop()     raise ValueError('Timeout') else:     if getting.resp_data:         r = getting.resp_data     else:         if getting.exception:             raise ValueError('REquest Exception')         else:             raise ValueError('Undefined exception') 

And all works fine, but sometime I start catching this exception:

error: can't start new thread 

at the line of starting new thread:

getting.start() 

and the next and the final line of traceback is

File "/usr/lib/python2.5/threading.py", line 440, in start     _start_new_thread(self.__bootstrap, ()) 

And the answer is: What's happen?

Thank's for all, and sorry for my pure English. :)

Answer 1

The "can't start new thread" error almost certainly due to the fact that you have already have too many threads running within your python process, and due to a resource limit of some kind the request to create a new thread is refused.

You should probably look at the number of threads you're creating; the maximum number you will be able to create will be determined by your environment, but it should be in the order of hundreds at least.

It would probably be a good idea to re-think your architecture here; seeing as this is running asynchronously anyhow, perhaps you could use a pool of threads to fetch resources from another site instead of always starting up a thread for every request.

Another improvement to consider is your use of Thread.join and Thread.stop; this would probably be better accomplished by providing a timeout value to the constructor of HTTPSConnection.

Answer 2

You are starting more threads than can be handled by your system. There is a limit to the number of threads that can be active for one process.

Your application is starting threads faster than the threads are running to completion. If you need to start many threads you need to do it in a more controlled manner I would suggest using a thread pool.